Vinyl acetate (VA) is an important chemical product, and its production process comprises a rectification step which usually generates a bottom residue in distillation kettle after the rectification. This bottom residue is a complex viscous tar-like mixture (usually is called as “kettle bottom residue of vinyl acetate”, “tar”, “pulp black liquid”), comprises polyvinyl acetate and free acetic acid as main components as well as copolymers with functional groups such as carboxyl and hydroxyl groups, and has a strong sharp smell of acetic acid. The Ministry of Environmental Protection of China had listed the bottom residue as “hazardous solid waste”. The bottom residue is usually treated in an incineration way by VA preparations. Since the direct combustion thereof may pollute atmosphere, it is required by environmental protection regulations that the bottom residue must be incinerated with a specific oxygen enriched combustion device, which will increase the investment and operation costs of VA preparations. In the meantime, the recyclable resources in the bottom residue are abandoned by incineration as well.
Chinese patent application CN1231296A discloses a method for preparing a vinyl resin from a kettle bottom residue of vinyl acetate. International patent application WO2005/039729A (corresponding to Chinese patent application CN1764494A) under PCT discloses a method for treatment of a kettle bottom residue of vinyl acetate by washing with water repeatedly. Chinese patent application CN1736974A discloses a method for treatment of a kettle bottom residue of vinyl acetate by distillation with a specific distillation kettle.
However, it is still in need to develop methods for recycling a kettle bottom residue of vinyl acetate in order to sufficiently utilize resources, provide more products and reduce environmental pollution.